1.1 (B) Shows The Transformational Stereoisomer Of Butane

Conformational stereoisomer of butane
Butane, C4H10 is an alkane with four carbon atoms which are bonded to each other by single bonds. Butane can form two isomers which are n-butane and isobutane. Figure1.1(a) and 1.1(b) shows the structures of n-butane and isobutane.
Alkanes usually show conformational isomerism due the presence of C-C single bonds. It is important to understand that conformational isomer can only occur in compound with single bond but not double or triple bond. This is because only single bond allows free rotation among the atoms as it has lower energy. Compare to double bond which has higher energy that cause restriction of rotation, breaking the bond to allow rotation is mostly impossible.
The rotations of isobutane on the axis of C-C bond can be seen in many angles’
The stability of the conformations can be explained by focusing on staggered and eclipsed conformers. Staggered conformers are with dihedral 60 degrees, and the hydrogen atoms of C-1 are far from the hydrogen atoms of C-2. Staggered conformers include anti-conformation and gauche conformation. Eclipsed conformers are which the hydrogen atoms of C-1 are lined up with the hydrogen atoms of C-2. Refer back to Table 1.2 which clearly shows the structure explain the staggered and eclipsed conformers. Staggered conformers are more stable than eclipsed conformers due to distribution of hydrogen atoms which can lead to steric hindrance. The hydrogen atoms in staggered conformers are further away from one another compare to the hydrogen atoms in eclipsed conformers which are near or in-line with one another. As had mentioned at above, the further the hydrogen atoms, the more stable the conformation due to less steric hindrance between the same